<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
<script>
    let num = '10';
    console.log(num, typeof num)
    let b = true
    console.log(b, typeof b)
    let c = null
    console.log(c, typeof c)
    let d
    console.log(d, typeof d)

    let arr = [1, 2, 3, 4, 5]
    console.log(arr, typeof arr)
    console.log(arr instanceof Array)
    console.log(num instanceof Array)

</script>
</body>
</html>
